Lidar Mapping Systems Post Processing - Applying a Geoid in Terrasolid Revision Date: May 14, 2019

LiDAR Mapping Systems Post Processing - Applying a Geoid in TerraSolid Revision Date: May 14, 2019

Phoenix LiDAR Systems 10131 National Blvd. Los Angeles, CA 90034 www.phoenixlidar.com +1.323.577.3366 [email protected]

Legal Notices

All the features, functionality, and other product specifications are subject to change without prior notice or obligation. Information contained herein is subject to change without notice.

Please read carefully and visit our website, w ww.phoenixlidar.com for further information and support.

NOTE: This brief provides a description of the workflow for applying a geoid file to a dataset in the United States. Your location and the product(s) you purchased may not support certain functions dedicated to specific models, upgrades or software.

Disclaimer

Information in this document is provided in connection with Phoenix LiDAR Systems products. No license, expressed or implied, by estoppels or otherwise, to any intellectual property rights is granted by this document. Except as provided in the terms and conditions of sale for such products, Phoenix LiDAR Systems assumes no liability whatsoever, disclaims any express or implied warranty, relating to sale and/or use of products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.

Phoenix LiDAR Systems products are not intended for use in medical, life saving, life sustaining, critical control or safety systems, or in nuclear facility applications. In no event shall Phoenix LiDAR Systems liability exceed the price paid for the product from direct, indirect, special, incidental, or consequential damages resulting from the use of the product, its accompanying software, or its documentation. Phoenix LiDAR Systems makes no warranty or representation, expressed, implied, or statutory, with respect to its products or the contents or use of this documentation and all accompanying software, and specifically disclaims its quality, performance, merchantability, or fitness for any particular purpose. Phoenix LiDAR Systems reserves the right to revise or update its products, software, or documentation without obligation to notify any individual or entity. Backup collected data periodically to avoid any potential data loss. Phoenix LiDAR Systems disclaims any responsibility of all sorts of data loss or recovery.

Applying a Geoid in TerraSolid

The Phoenix LiDAR Systems’ Post Processing workflow creates LAS/LAZ in Ellipsoidal height, but if data is required to have orthometric height values, a geoid can be applied in the final stages of post processing in TerraSolid.

1 Prepare Data for use in TerraScan

1.1 Download Continental United States Geoid model from Phoenix LiDAR Systems

Download the Continental US Geoid 12B LAZ file that has been optimized for use in TerraScan on our website at: Client Links > Downloads > Geoids

This Geoid file is only applicable for the continental United States. Projects in other areas will require custom Geoid file with proper latitude, longitude, and dz values. Please contact [email protected] if you need a geoid model for TerraSolid.

1.2 Coordinate ranges, Projection systems, and Bounding delineation

Use TerraScan to read all the points in the project. If the project contains too many points to load all at once, read a representative tile (a center tile). In the dialog that pops up first, note the Easting and Northing origin of the data in its local projection system.

Coordinate origin of a LAZ file (in its local projection system)

Go to the TerraScan toolbar and locate the main toolbar and open “Scan Define Coordinate Setup”. Ensure the resolution is at least 1000 (mm scale resolution) and that the Easting and Northing Origin will contain the coordinate origin of the data.

TerraScan’s Define Coordinate Setup

Use the ‘place shape’ or ‘draw fence’ tool to create a bounding box around the project area. The geoid file is very sparse, so this delineation needs to be at least 5x larger than your project area. This will ensure that TerraScan will have enough points to apply a valid model to the project needing a geoid adjustment.

Bounding box for loading the Geoid file

1.3 Preparing Geoid Model

Highlight the bounding box created earlier and use TerraScan to ‘read points’. All geoid files distributed by Phoenix LiDAR Systems are in WGS84, and need be transformed/projected to match your LiDAR data’s datum/projection. You will likely apply the same transformation/projection used while importing your trajectory.

Load the Geoid LAZ and in the ‘read points’ dialog, apply the proper projection to match the LiDAR dataset, and select ‘Inside fence only’.

Reading in the geoid file “Inside fence only”. The geoid is in WGS84 lat lon coordinates

Select the proper projection to match the lidar data

An alert will sometimes pop up saying that the first point is outside of the coordinate range, but click ok and disregard, as loading inside the fence alleviates this problem.

Click OK when alert dialog pops up

With the Geoid points loaded, use TerraScan to ‘Save points as’ and save the geoid points as an ENZ file and ensure the extension is .xyz.

Save points as ENZ (when naming the file, ensure .xyz is the extension)

2 Apply the Geoid in TerraScan

2.1 Applying the Geoid Model

Once the Geoid file has been loaded and saved for the general region of the project, the dataset is ready for the application of the Geoid. If the dataset is in a ‘Project’, use the “Define Project” dialog to use ‘Tools->Adjust to Geoid’, otherwise load all the LiDAR points in TerraScan and use the main TerraScan dialog: ‘Tools->Adjust to Geoid’. Select the Geoid.xyz file from the previous step. TerraScan will apply the dz values to the points by overwriting them, so if a backup is desired, make a copy prior to the ‘Adjust to Geoid’ step.

Applying a geoid to a loaded dataset

This content is subject to change. Download the latest version from www.phoenixlidar.com

If you have any questions about this document, please contact Phoenix LiDAR Systems by sending a message to [email protected].